This invention relates to a bearing housing and seal structure cooled by a combination of air and oil cooling means. The combination of air and oil cooling prevents coking of the oil supplied to lubricate those bearings and seals which must continue to function in a hot environment. Oil has been known to carbonize or coke at the 600.degree. F. temperatures often reached in a turbine engine. This makes it difficult to supply proper lubrication to the bearings which support the turbine stages of a gas turbine engine.
Coking is defined as the carbon residue left when oil evaporates due to high temperatures.
Because of the intense heat developed within the combustion sections of a gas turbine engine, it is necessary to arrange for cooling of the oil flowing through the lubricating passages. It is common practice to use a pressurized closed circuit lubrication system in a turbine engine. After oil has been supplied to components requiring lubrication, it drains into a sump. Most oil lines are cored or drilled passages. Oil draining from the bearings into the sumps is returned to a reservoir through a scavenge pump. Oil is taken from the reservoir by the pressure section of the pump and made to flow through a cooler, a filter and thence through service lines to the gears and bearings requiring lubrication.
Because of the air (and gas) pressures that exist in a gas turbine engine during operation, provisions must be made to control air leakage into bearing areas. A wide variety of seals are successfully used to control both air and oil leakage across the mating rotating surfaces. However, often problems are encountered in the turbine section of an engine which is immediately downstream from the combustor.
To achieve better engine operating efficiencies, that is, lower the specific fuel consumption, combustion temperatures have been raised. As a result, the hot gases passing through the turbine flow path are operationally hotter in the new engines than was the case with engines previously being produced. The higher operating temperatures result in higher temperature environments at both the seals and the bearings within the turbine section of the engine. When the heat transferred from the structure to the lubricating oil flowing therethrough is such that the temperature of the oil is raised above the boiling point, coking results. Carbon residues damage the seals and deterioration of the engine ensues. According to this invention, means are constructed to reduce the operating temperatures of the inner support structures for the bearing package in the turbine section of a gas turbine engine to levels which prevent coking of the lubricating oil. This is accomplished by incorporating a combination of air and oil cooling of this structure.